The present invention relates to an apparatus and method for controlling the output power of a generator and particularly to an apparatus and method for keeping the generator temperature below an allowed limiting value.
An apparatus for control of generator output power is known including an exciting winding of a generator, a voltage regulator connected with the generator, which controls the output power of the generator by influencing the excitation current in the exciting winding of the generator and means for temperature measurement.
An A.C. alternator, which produces an alternating voltage, is predominantly currently used in motor vehicles to supply electrical power. The alternating voltage produced by the alternator is rectified in a connected rectifying device for supplying direct-current consuming devices and for charging a battery. Since the output voltage of the generator depends considerably on the generator speed, a voltage regulator is used to provide the desired constant output voltage, which influences the excitation current of the generator, so that the generator voltage is held at a constant value, which in the typical motor vehicle power supply system is 14 volts D.C., despite considerable changes in the generator speed.
Since the number of electrical energy-consuming devices in motor vehicles is continually growing, the requirements for generators are always increasing. Particularly in winter, when window heaters are turned on in addition to the standard consuming devices or when the motor vehicle spends a longer time in city traffic, and also when the generator is operated at a slower rotation speed, energy supply problems develop. For this reason the current generated by the A.C. alternator has been increased, so that the power output of the generator is greater at the same voltage.
One possibility, which increases generator power, is described in German Published patent Application 31 42 878. According to this suggestion, the exciting winding is provided with a voltage increased relative to the battery voltage. Because of that the strength of the exciting current is increased, since a substantially greater magnetic field is produced, which leads to an increase of generator output power with generator dimensions otherwise unchanged. The maximum exciting current and/or the maximum flow is determined by the limiting temperature of the rectifier diodes and/or the stators in the generator. If, as described in German Published Patent Document 31 42 878, the exciting winding operates with a comparatively greater voltage relative to the power supply voltage, there is a danger that the temperature limit may be exceeded during harmful or damaging operating conditions.